﻿GLABEOUS MONTIPORiE. 43 



branches seem to die away in any part, not necessarily at tlie base, and are then coated over 

 again by a thin layer of living coral. 



Tliis coral is said (on Quelch's original labels) to be "the most abundant reef-forming 

 species on the island of Mactan, Zebu." 



a. Mactan Island. H.M.S. ' Challenger.' [86. 12. 9. 255.] 



I. Mactan Island. H.M.S. ' Challenger.' [86. 12. 9. 357.] 



c. (A fragment fitting on to a.) 



25. Montipora alcicornis. (PI. XXXII. fig. 10.) 



Description. — Corallum groves out into thin crooked stems which widen into irregular 

 elks' horn-shaped expansions 4 to 5 cm. across. From these expansions, one of the usually 

 short blunt prongs runs out and again widens. 



Calicles very numerous, varying in size from • 5 mm. and under, like pinholes in the 

 smooth surface. Septa as six thin, sharp, and toothed ridges projecting but a very little way 

 into the fossa. The margin of the calicle is generally sharply defined by a continuous neatly 

 petaloid rim. 



Ccenenchyma consists of a laminate reticulum which streams along the axes of the 

 branches. The transition between this and the cortical layer is gradual, the latter layer 

 being also decidedly flaky, the pores being in many cases neatly round or oval. Except at 

 the growing tips and on the upper surfaces of the sloping branches, the ccenenchyma is 

 smooth, but is lined all over in an irregular pattern by the thickened white upper edges of the 

 bands of the reticulum. On the upper surfaces above mentioned, the thin walls forming the 

 petaloid rims rise slightly so that a narrow irregular jagged furrow runs between the calicles. 



The single specimen formed an extensive tangle of dead and living branches wliich grew 

 at a small angle with the horizon, being depressed by the large flat growth of M. calcarea. 

 Wherever the edge of this latter coral rests upon the " elks' horns " of its branching congener 

 its ccenenchyma foams up in a wonderfully rich manner (see PI. X. on the left, also p. 59) ; 

 perhaps the support relieved it of the necessity of thickening and strengthening its substance 

 for free horizontal growth. 



This coral differs from the last type in the much smaller average size and comparative 

 inconspicuousness of the calicles, and in the much finer texture of the surface ccenenchyma. A 

 comparison of the descriptions will show how near the two approach in essential features, 

 and it may be that the differences are due to the unfavourable position in which the specimen 

 here described has grown. 



It differs also from the specimens of M. gaimardi, which are from the same locality, and 

 are also ramose, in the total absence of the six slightly projecting conspicuous septa, in the 

 characters of the surface ccenenchyma, and in the method of growth. 



The peculiar white chalkiness which characterises M. calcarea, though slightly less marked, 

 is seen here also, although it is not in the Tonga specimens of M. gaimardi. Tliis variation 

 is probably due to some purely local conditions of the environment.* 



* On the suggestion that these are corroded specimens, see on M. calcarea, p. 60, and M. Ursula, 

 p. 165. 



G 2 



